Electrical apparatus



July 7; 1925. 1,545,207

C. G. SMITH ELECTRICAL APPARATUS Filed Aug. 50, 1920 Patented J.'.1y1 ,192s. v a p 1,545,207 f UNITED" STATES PATENT- OFFICE.

CHARLES .G. smrn, or mnnronn, m'ssacnusm'rs, assrenon, BY nnsma assummmrrs, 'ro S-TUBE oonrom'rzon, or novnn, DELAWARE, A conroaa'rron or DELAWARE.

. ELECTRICAL APPARATUS.

Application filed August 30, 1920. Serial No; 406,886. To all it may concern: prevent conduction through the gas between Be it known that I, CHARLES G; SMITH, a the juxtaposed surfaces of the electrodes citizen of the United States, residing at Medwith relatively high potential differences and ford, in the count of Middlesex and State gas pressures corresponding to one oneof Massachusetts, have invented certain new hundret-h of a millimeter of mercury, or

anduseful Improvements in Electrical Apmore. paratus; and -I do hereby declare the follow- It will be seen that this invention involves ing to be a full, clear, and exact description principles not heretofore embodied in the of the invention, such as will enable others usual type of low pressure gaseous discharge 10 skilled in the art to which it appertains to apparatus. With my invention it is possible make and usethe same. Y to impress extremely high potential gradi- The present invention relates to electrical ents in the gas without causing conduction apparatus and more particularly to appa- 'between juxtaposed surfaces. ratus of this character involving electrical A simple and efficient application of my 15 circuits which include a gaseous medium as invention is embodied in a vacuum condenser part of the circuit. aving two concentric metal tubes of cylin- I have discovered that it is possible by drical form positioned and located by suitthe proper design and location of electrodes ably designed insulating supports, and all immersed in a gas to insulate and restrict enclosed within a gas-filled receptacle of in conduction'through the gas even though the sulating material. The arrangement of the space separating the electrodes is subjected tubes which are at different potentials is such to a high potential gradient. I accomplish that the distance through the gas between this result by making the space between juxall juxtaposed surfaces at different potential taposed surfaces of the electrodes sufliciently gradient is sufliciently short to prevent gasshort to prevent initiation of substantial eous conduction. In this particular embodiconduction directly across said space by po- Inent all available aths for the dischargeof tentials high enough to initiate conduction electrons throught e gaseous medium are of across longer gaps, and at the same time prethe order of magnitude of the mean free venting substantial conduction between the path of the electrons, and all paths through non-opposed or back areas of the electrodes the insulating material are sufiiciently long around the boundary of said space. In the to prevent breakdown and consequent dispresent instance the surfaces of the coopercharge therethroug ating electrodes are spaced apart a distance The accompanying drawing illustrates in which is comparable to and of the order of section a vacuum condenser embodying the 35 magnitude of the mean free paths of elecinvention.

trons in the gas in which the electrodes are The illustrated embodiment of the invenimmersed. This meanfree path may be detion discloses a vacuum condenser embodyfined asthe average distance which an elecing a plurality of electrodes or plates at diftron travels at ionizing velocity before ionizferentpotentials, all immersed in a gas, the 40 ing impact with a gas molecule (or atom). plates being designed and located in such a 95 The value of thismeanfree path in any given manner that the only paths available for gas is affected by the pressure under which short circuit through the gaseous medium the gas is placed. By a particular design are too short to permit the initiation of elecand location of cooperating electrodes, in tron discharge. According to thisdesign, the present instance two cylindrical tubes of the condenser" will not break down by disdifferent diameters concentrically located, I charge under'a potential difference of 10,000 can insure that all paths available for disvolts, even when the gas in which the elecchargc through the gas are short and of the trodes or plates are immersed is at a pressure order of magnitude of the mean free paths as great as of a millimeter. of electrons in the gas and by proper design Upon referring to the accompanying of the insulating and supporting dielectric I drawing, it will be observed that the concan insure that all paths through the dielecdenser comprises two concentric cylinders 10 trio are sufficiently long to prevent breakand 12 of conducting material, enclosed down under the applied voltage. within a gas-filled receptacle 14 of glass or With such a construction, it is possible to other insulating material. The tubes 10 and no 12 are retained in concentric relation by in sulating supports 16 and 18. Each of these supports, as shown, is provided with an enlarged base portion 20, fitting within and 15 holding the outer tube 12, and a smaller head portion 22, fitting within the inner tube 10. In addition the insulating supports may be provided with a reduced neck 24, which provides an insulating gap between the end of the inner tube or cylinder and the insulating. support. As will be observed, with this construction all direct paths for electron discharge between the surfaces of the cylinders at different potentials are short, and in addition all paths available for discharge between these surfaces through the insulating support are long. As will be observed from an inspection of the drawing, the lower insulating support 18 may be 20 conveniently provided-with a base 26 fitting closely within the receptacle 14 and held therein in any suitable manner. With this construction, the cylinders are held in the proper positions within the receptacle. The circuit leads niay be conveniently disposed, as shown, the connection with the outer tube 12 being indicated at 28 as attached to the upper edge of the tube, and the connection for the 'inner'tube being indicated at 30 as 30 attached to the inner surface of the tube between the insulating supports, passing outwardly through the insulating supports and the opposite end of the tube. The condenser may obviously be included in any desired form of circuit.

The theory underlying the operation of this device may be stated briefly as follows: The conductivity of a gas atany instant may be said to depend upon the number of ions present. This number is usually small but is rapidly increased by ionization by collision upon impressing a sufficientpotential gradient. In addition, the dis tribution is such as to make the conductivity of the gas under pressure, or with only'a partial Vacuum, relatively good. The presence of these ions which render the gas conductive is due to the collision of electrons or ions with atoms or molecules, resulting in the ,production of more ions, which in turn collide with other atoms, and continue to produce still more ions. If the electrons given off from one electrode have normally only a short distance to travel before arriving at the opposite electrode, their chances for collision are small, providing that the distance of separation of the electrodes is suificiently short. It has been found possible to so proportion the distance which the electrons will travel that there are not a sufficient number of collisions between electrons and atoms to produce a sufficient number of positive ions to bombard the cathode and liberate electrons for the initiation of substantial gaseous conduction. Although in practice there are u11- doubtedly! some stray positive ions, always present, it is a fact that with the distance properly designed, as hereinbefore indicated, thelr number is insufiicient to give rise to, further positive ions and cause substantial'm gaseous conduction to take place.

It is believed that this theory is substantially correct as stated, but independently of the correctness of the theory, it is a fact that by designing and locating the electrodes in such a manner that the direct paths for electron discharge through the gaseous medium between juxtaposed surfaces of the electrodes are relatively short and of the order of magnitude of the mean free path of the electrons it is possible to insulate with a relatively poor vacuum the same differences of'potentia-l that previously required a substantially perfect vacuum.

It is believed that for best resultsthe length of said direct paths through the gas between juxtaposed surfaces of the electrodes at different potentials should be shorter than the mean freepath of the electrons; but owing to the difiiculty of exactly estimating the length of the mean free path, it is only known absolutel that the length of the available paths s ould be comparable to the mean free path of the electrons, and it may be possible to construct an insulating gap according to my new discovery even though the length of the available paths is as great, or greater, than the length of the mean free path and still be within the scope of the invention so long as these paths are sulficiently short to prevent substantial ionization.

From the foregoing it will be evident that each of the insulation blocks 16 and 18 constitutes an obstruction at one boundary of the space between the juxtaposed surfaces of the electrodes which prevents substantial conduction around the boundary between surfaces of the electrodes outside said boundary. In the illustrated embodiment said boundary may be considered to be an imaginary ring extending from one end of electrode 10 to the electrode 12 in the radial .plane of the end of electrbde 10. This obstruction may be spaced from the electrode as at 24 or when formed of insulation it may contact with the electrode as at 20. This obstruction is shaped and arranged to afford no path between the two electrodes along its surfaces as short as the shortest distance between the juxtaposed surfaces of the electrodes and in the illustration the shortest path between the electrodes along its surface is more than ten times the shortest distance between the two electrodes.

vAn important characteristic of the present invention consists in that one electrode is hollow and the other electrode has a surface presented to the interior surface of the hollow electrode, the areas of the two surfaces being unequal.

' sufiiciently short and the gas By making the surfaces of the two electrodes unequal in area the resistance of the ing direct current circuits where a condenser has a greater tendency to break down in one direction than in the other diIQCtIOIL It should be understood that the present invention is not limited inits application to the particular embodiment here shown, but is susceptible of'embodiment in a wide-variety of electrical circuits embodying gaseous mediums.

Havin thus described the invention, what is claime is:

1. Electrical apparatus comprising an electrode havin an extended surface area, and a second e ectrode havin an area of lesser extent presented to sai area across an intervening space, the space between juxtaposed surfaces of the electrodes being ressure bein sufficiently low to prevent initiation of substantial conduction directly across said space by potentials high enough to initiate conduction across longer aps, and means for preventing substantia conduction between other areas of said electrodes around the boundary of said space.

2. Electrical apparatus comprising an electrode having an extended surface area, and a second electrode of different size presented to said area across an intervening space, the space between juxtaposed surfaces of the electrodes being sufliciently short and the gas pressure being sufliciently low to prevent initiation of substantial conduction directly across said space by potentials high enough to initiate conduction acros longer "a s.

c iilElectrical apparatus comprising a hollow electrode and a second electrode presented tothe interior surface of the hollow electrode across an intervening space, the space between juxtaposed surfaces of the electrodes being sufficiently short and the gas pressure being sufliciently low to revent initiation of. substantial conduction irectly across said space by potentials high enough to initiate conduction across longer gaps, and means for preventing substantial conduction between the exterior surface of said hollow electrode and the second electrode. a 4. Electrical apparatus comprising an electrode havin an extended surface area, and a second e ectrode presented to said-area across an intervening space, the s ace between juxtaposed surfaces of the e ectrodes being sufliciently short and the gas pressure bein sufiiciently low to of slfimtantial conduction irectl across said space by potentials high enoug to initiate revent initiation conduction across longer gaps, and an obstruction adjacent boundaries of said sur-v faces, the obstruction extending sufficiently close to each electrode to revent substantial conduction around the oundary of said space and the obstruction being shaped and arranged to afford no path between the two electrodes along-its surface'as short as the shortest distance between said juxtaposed surfaces across said space.

5.- Electrical ap aratus comprising a hollow electrode an sented to the interior surface ofthe hollow electrode across an intervenin space, the

s ace between juxtaposed sur aces of the e ectrodes being sufficient] short and the gas pressure being sufficient y low to prevent nitiation of substantial conduction directl across said space by potentials high enoug 1 to initiate conduction across longer gaps, and an obstruction adjacent boundaries of said surfaces, the obstruction extending sufficiently close to each eQctrode to prevent substantial conductionbetween the electrodes around the boundary of said space.

6. Electrical apparatus comprisin two non-filamentary electrodes of di erent shapes with a rarified gas space therebetween, one electrode having. an extended surface area presented to the other electrode, the space-between juxtaposed surfaces of the electrodes being sufficiently short to prevent initiation of substantial conduct-ion directly across said space by potentials high enough to initiate conduction across longer i Electrical apparatus comprising two non-filamentary electrodes formed of solid material with a rarified gas space thereb'etween, one electrode being hollow and the other electrode being presented to the interior surface thereof, the space between juxtaposed surfaces of the electrodes being sufficiently short to prevent initiation of substantial conduction directly across said a second electrode pre-" 1' space by potentials highenough to initiate" conduction across longer gaps, and means for preventing substantial conduction between the exterior surface of said hollow electrode and the second electrode.

8. Electrical apparatus comprisin two non-filamentary electrodes formed 0 solid material with a. gas space therebetween, one electrode having an extended surface area resented to the other electrode, the space tween juxtaposed surfaces of the electrodes being sufficiently short and the gas pressure being sufliciently low to prevent initiation of substantial conduction directly across saidspace by potentials high enough to initiate conduction across longer gaps, and insulation adjacent boundaries of said surfaces, the insulation extending sufiiciently close to each electrode to prevent substantial conduction between the electrodes around the boundary of said space and the shortest distance between the electrodes along the surface of the insulation being longer than the shortest distance between said juxtaposed surfaces across said space.

9. Electrical apparatus comprising two non-filamentary electrodes with a gas space therebetween, one electrode being hollow and the other electrode being presented to the interior surface thereof, the space between juxtaposed surfaces of the electrodes being sufliciently short and the gas pressure being sufficiently lowto prevent initiation of substantial conduction directly across said space by potentials high enough to initiate conduction across longer gaps, and insulation adjacent boundaries of said surfaces, the insulation extending sufiiciently close to each electrode to prevent substantial conduction between the electrodes around the boundary of said space.

10. Electrical apparatus comprising a hollow electrode having an open end and a second electrode presented to the interior surface of the hollow electrode adjacent said end, with a rarified gas space therebetween, the space between juxtaposed surfaces of the electrodes being sufliciently short to prevent initiation of substantial gaseous conduction between said surfaces by potentials high enough to initiate conduction across longer gaps, and insulating material substantially closing said open end of the hollow electrode.

11. Electrical apparatus comprising -electrodes having juxtaposed surfaces with a gas space therebetween, and insulation material extending sufficiently close to boundaries of said surfaces to prevent substantial conduction between the electrodes around the boundary of said space, the shortest distance between electrodes along the surface of the insulation being sufliciently long to prevent substantial conduction between electrodes along the surface of the insulation, and the space between juxtaposed surfaces of the electrodes being sufliciently short and the gas pressure being sufficiently low to prevent initiation of substantial conduction directly across said space by a potential at which conduction is resisted by said insulation.

12. Electrical apparatus comprising electrodes having opposed surfaces of different areas with a gas space therebetween, said space being comparable in length to the mean free path of electrons in the gas, and insulation disposed at boundaries of said surfaces, said insulation extending sufliciently close to each electrode to prevent substantial conduction between the electrodes around the boundary of said space.

13. Electrical apparatus comprising electrodes having opposite surfaces with a gas space therebetween, said space being comparable in length to the mean free path of said insulation extending tial conduction between the electrodes around the boundary of said space.

14. Electrical apparatus comprising electrodes having opposite surfaces with a gas space therebetween, one dimension of said space being comparable to the mean free path of electrons in the gas, and insulation confining said space in another dimension, substantially from one electrode to the other and the shortest distance between the electrodes alon the confining surface of the insulation eing longer than said dimension.

15. Electrical apparatus comprising electrodes having opposite surfaces with a rarified gas space therebetween, .one electrode surrounding a part of the other electrode, and insulating material disposed at boundaries of said surfaces, said insulating material extending sufliciently close to each elec-.'

trode to prevent substantial conduction between the electrodes around the boundary of said space and the shortest distance between electrodes along the surface, of the insulation being greater than the shortest distance between electrodes across said space.

16. Electrical apparatus comprising electrodes having therebetween a rarified gas gap of such length as to restrict gaseous conduction along the shortest path between the electrodes, and means for obstructing gaseous discharge along long paths includ- 'ing insulation extending along one electrode in close juxtaposition thereto.

17. Electrical apparatus comprising two concentric electrodes of solid conducting material, a gas-filled receptacle enclosing the electrodes, insulation for retaining the .electrodes in concentric relation, the space between juxtaposed.surfaces of the electrodes being sufliciently short and the gas ressure being sufiiciently low to prevent initiation of substantial gaseous conduction directly across the space by potentials high enough to initiate conduction across longer P 18. An electrical apparatus comprising two concentric tubes of conducting material, a gas-filled receptacle enclosing the tubes, insulating supports for retaining the tubes in concentric relation, the surfaces of the tubes at different potentials being spaced apart a distance which is short and of the order of magnitude of the mean free path of the electrons in the gas.

19. An electrical apparatus comprising a gas-filled receptacle, concentric tubes of conducting material fitted within the receptacle, means'for retaining the tubes in con-- centric relation, and separated by a disand tance less than the normal mean free path of the electrons through the gas to normally revent gaseous conduction across the gap etween the tubes.

20. Electrical apparatus comprising electrodes having opposite surfaces with a gas space therebetween, one dimension of said space being comparable to the mean free path of electrons in the gas, and insulating material confining said space in another dimension, said insulating material contacting with one electrode at the boundary of its said surface and having its confining surface spaced from the other surface a distance comparable to said mean free path.

21. Electrical insulating apparatus comprising a hollow electrode and a second electrode disposed within said hollow electrode presented to the interior surface of the hollow electrode across an intervening tentials high enough to initiate conduction across longer aps, ing substanti. terior surface of said hollow electrode and the second electrode.

22. A condenser comprising a gas-filled receptacle, concentric tubes of conducting material fitted within the receptacle, means for retaining the tubes in concentric relation, and separated by a distance less than the normal mean free path of the electrons through the gas to normally prevent gaseous conduction across the gap between the tubes in both directions.

CHARLES G. SMITH.

and means for preventconduction between the ex- 

